Three-dimensional force measurements in optical tweezers formed with high-NA micromirrors

Abstract

The three-dimensional trap stiffness of optical tweezers formed with high-NA micromirrors is investigated by back-focal-plane interferometry and power spectrum analysis. Normalized stiffness values of � xy/P trap =1.2��N/m�/mW and � z/P trap=0.52��N/m�/mW in the transverse and axial directions, respectively, have been measured for polystyrene spheres with a radius of 1.03 �m. Compared with high-NA microscope objectives, micromirrors achieve much better trapping performances, particularly in the axial direction